1. Field of the Invention
The present disclosure relates to a fan driver system and an analog fan drive chip, more particularly to an analog fan drive chip capable of automatically detecting a type of a fan.
2. Description of the Related Art
With progress in electronic technologies, various electronic devices (such as processor, display card or other device) have higher and higher working frequencies and power consumption, but also generate more heat during operations. In order to prevent the devices from being damaged because of overheat, cooling devices are usually required to decrease temperatures of these devices. Generally, fans are cooling devices widely used. A fan is usually disposed near the electronic device to be cooled, and configured to generate air flow around the electronic device for heat dissipation. The fan operated in a higher speed can blow hot air away from the electronic component more quickly, so as to provide higher cooling efficiency. Currently, commercially available fans can be classified into three-wire direct current (DC) fan and four-wire pulse width modulation (PWM) fan. According to a specification defined by the INTEL Corporation, the four-wire PWM fan must be provided with a built-in pull-up resistor. However, many four-wire PWM fans which do not meet the requirement of the specification of the INTEL Corporation are also commercially available. That is, some commercially available four-wire PWM fans do not have the built-in pull-up resistor.
Please refer to FIG. 1 which shows an interface 102 of a general three-wire DC fan 104. The interface 102 includes a ground terminal 106, a DC signal terminal 108 and a speed signal terminal 110. The speed signal terminal 110 is configured to provide a speed signal of the fan, and the speed signal is a square wave having a frequency proportional to the speed of the three-wire DC fan 104. The speed of the three-wire DC fan 104 can be controlled by the voltage input in the DC signal terminal 108. During operation of the fan, the voltage applied to the DC signal terminal 108 is adjustable, for example, in a range from 4V to 12V, for fan speed control. The speed of the three-wire DC fan 104 is positively relevant to amplitude of the voltage applied to the DC signal terminal 108. Higher the voltage input to the DC signal terminal 108 is, faster the speed of the fan is.
Please refer to FIG. 2 which shows an interface 202 of a general four-wire PWM fan 204. The four-wire PWM fan 204 may be provided with/without a built-in pull-up resistor. The four-wire PWM fan 204 has a ground terminal 206, a DC signal terminal 208, a speed signal terminal 210 and a PWM control terminal 212. The DC signal terminal 208 and the speed signal terminal 210 of the four-wire PWM fan 204 are similar to the DC signal terminal 108 and the speed signal terminal 110 of the three-wire DC fan 104. The speed of the four-wire PWM fan 204 is controlled by a duty cycle of the PWM signal applied to the PWM control terminal 212, but not the voltage applied to the DC signal terminal 208. For the four-wire PWM fan 204, the DC signal terminal 208 is usually kept as a fixed voltage. When the duty cycle of the PWM signal applied to the PWM control terminal 212 is 50%, the speed of the four-wire PWM fan 204 is 50% of a full speed of the four-wire PWM fan 204. Similarly, when the duty cycle of the PWM signal input to the PWM control terminal 212 is 80%, the speed of the four-wire PWM fan 204 is 80% of the full speed. That is, when the duty cycle of the PWM signal applied to the PWM control terminal 212 is increased or decreased, the speed of the four-wire PWM fan 204 is increased or decreased correspondingly.
Generally speaking, the electronic device is usually designed to just support a certain type of the fan, so the user is required to connect a correct type of the fan to the electronic device for better heat-dissipation performance; however, it is inconvenient for the user who does not know the type of the fan supported by the electronic device. For example, prior to selection of the fan for a computer, the user had better check a motherboard of the computer to know the supportable type of the fan.
In prior art, a tachometer is used to detect the type of the fan, so as to solve above-mentioned problem. The tachometer requires a clock signal to count a number of cycles of the speed signal of the fan in a preset period, but a clock circuit cannot be designed in an analog chip.